Phonons and free carriers in a strained hexagonal GaN-AlN superlattice measured by infrared ellipsometry and Raman spectroscopy

Conference · Sat Jul 01 04:00:00 EDT 2000

OSTI ID:20104609

Schubert, M; Kasic, A; Tiwald, T E; Woollam, J A; Haerle, V; Scholz, F

Phonon and free-carrier effects in a strained hexagonal ({alpha}) {l_brace}GaN{r_brace}{sub l}--{l_brace}AlN{r_brace}{sub m} superlattice (SL) heterostructure (l = 8 nm, m = 3 nm) are studied by infrared spectroscopic ellipsometry (IRSE) and micro ({micro})-Raman scattering. Growth of the heterostructures was performed by metal-organic vapor phase epitaxy (MOVPE) on (0001) sapphire. An unstrained 1 {micro}m-thick {alpha}-GaN layer was deposited prior to the SL. SL phonon modes are identified combining results from both IRSE and {micro}-Raman techniques. The shift of the GaN-sublayer phonon modes is used to estimate an average compressive SL stress of {sigma}{sub xx} {approximately} {minus}4.3 GPa. The IRSE data reveal a free-carrier concentration of n{sub e} {approximately} 5x10{sup 18} cm{sup {minus}3} within the undoped SL GaN-sublayers. According to the vertical carrier confinement, the free-carrier mobility is anisotropic, and the lateral mobility ({mu}{sub {perpendicular}} {approximately} 400 cm{sup 2}/Vs, polarization E{perpendicular}c-axis) exceeds the vertical mobility ({mu}{sub {parallel}} {approximately} 24 cm{sup 2}/Vs, E{parallel}c) by one order of magnitude.

• Research Organization: Univ. of Nebraska, Lincoln, NE (US)
• OSTI ID: 20104609
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ALUMINIUM NITRIDES
COMPOSITE MATERIALS
ELLIPSOMETRY
EXPERIMENTAL DATA
GALLIUM NITRIDES
MICROSTRUCTURE
RAMAN SPECTRA
STRAINS
VAPOR PHASE EPITAXY